THE GIST

- If ambient noise is too loud, whales may give up trying to communicate with each other altogether.

Noise pollution created by humans is forcing endangered North Atlantic right whales and other whale species to increase the amplitude of their calls in an attempt to be heard by each other over the din, according to a new study.

The paper, published in the latest Royal Society Biology Letters, provides the first evidence that baleen whales can modify the loudness of their calls in response to outside noise.

One downside is that "shouting," as for humans and other animals, requires more energy expenditure and probable strain, so we are making life more difficult for these already at risk marine mammals. Since communication is tied to mating, feeding and more, these critical aspects of whale life may also be impacted.

Another concern "is that when noise exceeds a certain level, right whales will not be able to increase their call amplitude enough to compensate," project leader Susan Parks told Discovery News.

Parks, a research associate in Pennsylvania State University's Environmental Acoustics Program, and her team placed acoustic recording suction cup tags on North Atlantic right whales in the Bay of Fundy during the summers of 2001, 2002 and 2005. The scientists took note of both the ambient noise and the whale calls.

"The predominant source of human generated noise in right whale habitats is from commercial shipping, resulting in a chronic noise source that overlaps the frequency range of right whale communication signals," according to the team.

For this study, the noisy ships were anywhere from around 62 to well over 621 miles away from the whales.

Parks compares the constant ruckus to us hearing sounds from cars going down a road.

"On a country road, a single car going by would increase the noise you experience for a short period of time," she said. "In contrast, standing next to a busy downtown road during rush hour would have both higher levels of noise and more continuous noise."

The whales really appear to struggle when the noise is the same frequency range of their calls. One affected form of whale communication is referred to as an "upcall." This is a sweeping sound, where the whale quickly goes from a high to low frequency, resulting in a short "whoop!"

Previous studies show that beluga whales and killer whales can also increase the loudness of their calls in noisy settings.

Parks, however, is quick to point out that her study only took place under moderate noise pollution conditions.

"Whales may stop calling all together when the noise levels increase," she warned.

Nature itself isn't always quiet, so whales have evolved a means of being heard over sounds like breaking waves, distant earthquakes and even the chitchat of other marine organisms. But human-produced sounds are more constant and loud than most any sound nature produces.

"(The study) is a real contribution to the jigsaw puzzle a small group of us are trying to piece together regarding how baleen whales are influenced by changes in their acoustic habitat as a result of human activities," Christopher Clark, director of the Bioacoustics Research Program at Cornell University, told Discovery News.

"In the area where Susan conducted this research, those activities are persistent and have increased by several orders of magnitude within the lifetimes of these whales," Clark added. "As she says, they can only compensate so much for the noise by calling louder."

"Think of this ocean noise situation as a loss of acoustic habitat, and just one in a set of impositions that our collective activities are imposing on the ocean ecosystem," Clark suggested. "Calling louder is just one of several responses right whales have to increases noise level; the more common response is to go quiet."